1. Field of the Invention
The present invention relates to a magnetic field generator for an MRI, and more specifically to an open type magnetic field generator for MRI.
2. Description of the Related Art
Related art in this kind is disclosed in the Japanese Patent Laid-Open No. 6-176917. An MR open-type magnetic apparatus disclosed in this Laid-Open comprises two magnet blocks each made of a plurality of magnets. The magnet blocks are spaced from each other for providing work space. Each of the magnet blocks includes an annular super-conductive coil cluster and a magnetic field enhancer. The two magnet blocks are supported by a generally C-shaped supporting frame made of nonmagnetic material such as stainless steel or aluminum.
However, there is a problem according to the above related art. Specifically, manufacturing is difficult because of the use of specially shaped supporting frame formed into a Roman character C, resulting in increased cost.
Another example of related art is disclosed but not detailed in the Japanese Design Registration No. 847566, Similitude No. 1.
It is therefore a primary object of the present invention to provide a magnetic field generator for MRI that is easy to manufacture at a lower cost.
A first magnetic field generator for MRI according to the present invention comprises a pair of plate yokes opposed to each other with space in between, a magnet provided in each of the opposed surfaces of the pair of plate yokes, a column yoke connected to the pair of plate yokes for magnetic connection of the pair of plate yokes, and an enhancing member made of magnetic material and provided in an inner surface of the connection between the column yoke and the plate yokes.
According to the first magnetic field generator, manufacturing can be performed easily and at low cost by simply connecting the pair of plate yokes to the column yoke so that the pair of plate yokes is opposed to each other with space in between, and attaching the enhancing member in an inner surface of the connection between the column yoke and the plate yokes. Further, the enhancing member is made of magnetic material, and therefore functions as part of the yoke, practically increasing cross section of the yoke at the connecting portion. This reduces leakage magnetic flux, providing a stronger magnetic field.
According to the first magnetic field generator, preferably the enhancing member has a curved slant face. This makes possible to provide a greater space for accommodating a patient, while improving operability of medical operations performed by a medical doctor. Further, preferably the enhancing member is provided in an inner surface of the connection between the column yoke and the plate yokes at a place farthest from the magnet. By providing the enhancing member at the farthest location from the magnet thereby increasing the distance between the enhancing member and the magnet, it becomes possible to prevent the magnetic flux generated by the magnet from short-circuiting to the enhancing member, eliminating the magnetic flux short circuiting, maintaining a uniform and strong magnetic field.
A second magnetic field generator for MRI according to the present invention comprises a pair of plate yokes opposed to each other with space in between, a magnet provided in each of the opposed surfaces of the pair of plate yokes, a column yoke connected to the pair of plate yokes for magnetic connection of the pair of plate yokes, and an enhancing member having a curved slant face and provided in an inner surface of the connection between the column yoke and the plate yokes.
According to the second magnetic field generator, manufacturing can be performed easily and at low cost by simply connecting the pair of plate yokes to the column yoke so that the pair of plate yokes is opposed to each other with space in between, and attaching the enhancing member in an inner surface of the connection between the column yoke and the plate yokes. Further, by using the enhancing member having a curved slant face, it becomes possible to provide a greater space for accommodating the patient, while improving operability of medical operations performed by the medical doctor.
According to each of the above mentioned generators, preferably the magnetic field generator further comprises a magnetic field adjusting bolt for adjustment of magnetic field by adjustment of relative position between the pair of plate yokes. By adjusting screwing depth of the magnetic field adjusting bolt, relative position between the pair of plate yokes can be adjusted, thereby adjusting the strength and distribution of the magnetic field.
A third magnetic field generator for MRI according to the present invention comprises a pair of plate yokes opposed to each other with space in between, a magnet provided in each of the opposed surfaces of the pair of plate yokes, a column yoke connected to the pair of plate yokes for magnetic connection of the pair of plate yokes, an enhancing member provided in an inner surface of the connection between the column yoke and the plate yokes, and a magnetic field adjusting bolt for adjustment of magnetic field by adjustment of relative position between the pair of plate yokes.
According to the third magnetic field generator, manufacturing can be performed easily and at low cost by simply connecting the pair of plate yokes to the column yoke so that the pair of plate yokes is opposed to each other with space in between, and attaching the enhancing member in an inner surface of the connection between the column yoke and the plate yokes. Further, by adjusting screwing depth of the magnetic field adjusting bolt, relative position between the pair of plate yokes can be adjusted, thereby adjusting the strength and distribution of the magnetic field.
Preferably, the magnetic field adjusting bolt includes a first bolt and a second bolt. The first bolt is screwed into the plate yoke with a tip of the first bolt contacting the enhancing member, and the second bolt is screwed into the plate yoke with a tip of the second bolt contacting an upper end face of the column yoke. Use of the first bolt and the second bolt as the magnetic field adjusting bolt makes possible to translate the plate yoke by adjusting the screwing depth of the first and second bolts.
Further, according to each of the magnetic field generators described above, preferably the magnetic field generator further comprises an engaging portion for engagement of at least one of the plate yoke and the column yoke with the enhancing member. By engaging the yoke with the enhancing member by the engaging portion, it becomes possible to provide better protection to the yoke from being out of alignment, making possible to shorten time required for re-adjusting the magnetic field distribution after the transportation.
A fourth magnetic field generator for MRI according to the present invention comprises a pair of plate yokes opposed to each other with space in between, a magnet provided in each of the opposed surfaces of the pair of plate yokes, a column yoke connected to the pair of plate yokes for magnetic connection of the pair of plate yokes, an enhancing member provided in an inner surface of the connection between the column yoke and the plate yokes, and an engaging portion for engagement of at least one of the plate yoke and the column yoke with the enhancing member.
According to the fourth magnetic field generator, manufacturing can be performed easily and at low cost by simply connecting the pair of plate yokes to the column yoke so that the pair of plate yokes is opposed to each other with space in between, and attaching the enhancing member in an inner surface of the connection between the column yoke and the plate yokes. Further, by engaging the yoke with the enhancing member by the engaging portion, it becomes possible to provide better protection to the yoke from being out of alignment, making possible to shorten time required for re-adjusting the magnetic field distribution after the transportation.
The above described objects and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of embodiments when taken in conjunction with the accompanying drawings.